A couple visited the Animal Resource Foundation in Chester, in Queen Anne's County around 4:30 p.m. Tuesday, a staff member named Kathy told NBC Washington.

They played with a miniature pinscher/dachshund puppy named Mango, as well as his two siblings.

“After about 40 minutes, the woman got up and left without saying anything,” said Kathy, who didn’t want her last name used. “The lady who was working here thought , ‘Oh that was weird’.”

The man stayed for a few more minutes, but staff members weren’t watching him closely. “We’re a very small staff and it’s hard to feed and walk [the pets] and all that [and supervise visitors,” Kathy said.

No one had ever tried to take an animal before, but after the man left, a staff member realized that seven-week-old Mango was missing.

“We do a background check [on adopters]; we’re very particular about who takes our animals,” she said.

Mango weighs less than two pounds, and hadn’t been weaned or wormed. He’s had only one of his necessary shots so far. And he’d already been spoken for -- a family had applied to adopt him, and were just waiting for him to get old enough.